The present invention relates to the delivery of drugs from stents coated with polymer. In particular the invention relates to delivery of matrix metalloproteinase inhibitors, for inhibition of restenosis following stent implantation in the treatment of cardiovascular disease.
A leading cause of mortality within the developed world is cardiovascular disease. Coronary disease is of most concern. Patients having such disease usually have narrowing in one or more coronary arteries. One treatment is coronary stenting, which involves the placement of a stent at the site of acute artery closure. This type of surgery has proved effective in restoring vessel patency and decreasing myocardial ischemia. However the exposure of currently used metallic stents to flowing blood can result in thrombus formation, smooth muscle cell proliferation and acute thrombotic occlusion of the stent.
Non-thrombogenic and anti-thrombogenic coatings for stents have been developed. One type of balloon expandable stent has been coated with polymers having pendant zwitterionic groups, specifically phosphorylcholine (PC) groups, generally described in WO-A-93/01221. A particularly successful embodiment of those polymers suitable for use on balloon expandable stents has been described in WO-A-98/30615. The polymers coated onto the stent have pendant crosslinkable groups which are subsequently crosslinked by exposure to suitable conditions, generally heat and/or moisture. Specifically a trialkoxysilylalkyl group reacts with pendant groups of the same type and/or with hydroxyalkyl groups to generate intermolecular crosslinks. The coatings lead to reduced thrombogenicity.
Fischell, T. A. in Circulation (1996) 94:1494-1495 describes tests carried out on various polymer coated stents. A thinner uniform polyurethane coating, having a thickness of 23 μm was observed to have a better performance than a relatively non uniform thicker layer having a thickness in the range 75 to 125 μm. The thicker coatings are further described by Van der Giessen, W J et al. in Circulation: 1996: 94:1690-1697.
It has been suggested to utilise coatings on stents as reservoirs for pharmaceutically active agents desired for local delivery.
In U.S. Pat. No. 5,380,299 a stent is provided with a coating of a thrombolytic compound and optionally an outer layer of an anti-thrombotic compound. The stent may be precoated with a “primer” such as a cellulose ester or nitrate.
Other drug containing stents and stent coatings are described by Topol and Serruys in Circulation (1998) 98:1802-1820.
McNair et al., in Proceedings of the International Symposium on Controlled Release Bioactive Materials (1995) 338-339 describe in vitro investigations of release of three model drugs, caffeine, dicloxacillin and vitamin B12, from hydrogel polymers having pendant phosphorylcholine groups. Alteration of the hydrophilic/hydrophobic ratio of the (hydrophilic) phosphorylcholine monomer 2-methacryloyloxyethyl phosphorylcholine, (HEMA-PC) and a hydrophobic comonomer and crosslinking of the polymer allows preparation of polymers having water contents when swollen in the range 45 to 70 wt %. Crosslinking is achieved by incorporating a reactive monomer 3-chloro-2-hydroxypropylmethacrylate. The tests are carried out on membranes swollen in aqueous drug solutions at 37° C. The release rates of the model drugs are influenced by the molecular size, solute partitioning and degree of swelling of the polymer. Dicloxacillin is found to have a higher half life for release than its molecular size would indicate, and the release profile did not appear to be Fickian.
McNair et al., in Medical Device Technology, December 1996, 16-22, describe three series of experiments. In one, polymers formed of HEMA-PC and lauryl methacrylate crosslinked after coating by unspecified means are cocoated with drugs onto stents. Release rates of dexamethasone from the stent, apparently into an aqueous surrounding environment, was determined. Drug release from cast membranes, as model coatings, showed that the release rate obeyed Fickian diffusion principles, for hydrophilic solutes. In the third series of tests, a non-crosslinked polymer coating, free of drug, coated on a stent, had a significant decrease in platelet adhesion when coated on a stent used in an ex-vivo arteriovenous shunt experiment. The stent coating method was not described in detail.
Stratford et al in “Novel phosphorylcholine based hydrogel polymers: Developments in medical device coatings” describe polymers formed from 2-methacryloyloxyethyl phosphorylcholine, a higher alkyl methacrylate, hydroxypropylmethacrylate and a methacrylate ester comonomer having a reactive pendant group. These PC polymers were investigated to determine the feasibility of delivering drugs and model drugs. Results are shown for caffeine, dicloxacillin, vitamin B12, rhodamine and dipyridamole. The device on which the drug is coated is a guidewire that is, it is not an implant.
In EP-A-0623354, solutions of drug and polymer in a solvent were used to coat Wiktor type tantalum wire stents expanded on a 3.5 mm angioplasty balloon. The coating weights per stent were in the range 0.6 to 1.5 mg. Coating was either by dipping the stent in the solution, or by spraying the stent from an airbrush. In each case coating involved multiple coating steps. The drug was for delivery to the vessel wall. The drugs suggested as being useful for delivery from stents were glucocorticoids, antiplatelet agents, anticoagulants, antimitotic agents, antioxidants, antimetabolite agents and antiinflammatory agents. The worked examples all use dexamethasone delivered from a bioabsorbable polymer.
In U.S. Pat. No. 5,900,246 drugs are delivered from a polyurethane coated substrate such as a stent. The polyurethanes may be modified to control its compatibility with lipophilic or hydrophilic drugs. Suitable drugs are antithrombotic agents, antiinflammatory agents such as steroids, antioxidants, antiproliferative compounds and vasodilators. Particularly preferred drugs are lipophilic compounds. A polyurethane coated stent is contacted with a drug in a solvent which swells the polyurethane, whereby drug is absorbed into the polyurethane. Selection of a suitable solvent took into account the swellability of the polyurethane and the solubility of the drug in the solvent. It was observed that lipophilic drugs loaded in this way released more slowly from hydrophobic polymer than more hydrophilic drugs, by virtue of interaction of the lipophilic drug with hydrophobic polymer.
In EP-A-0923953 coatings for implantable devices, generally stents, comprise an undercoat comprising particulate drug and polymer matrix, and an overlying topcoat which partially covers the undercoat. The top coat must be discontinuous in situ, in order to allow release of the drug, from the undercoat. Examples of drugs include antiproliferatives, steroidal and non steroidal antiinflammatories, agents that inhibit hyperplasia, in particular restenosis, smooth muscle cell inhibitors, growth factor inhibitors and cell adhesion promoters. The worked examples use heparin and dexamethasone. The polymer of the undercoat is, for example, hydrophobic biostable elastomeric material such as silicones, polyurethanes, ethylene vinyl acetate copolymers, polyolefin elastomers, polyamide elastomers and EPDM rubbers. The top layer is suitably formed of non-porous polymer such as fluorosilicones, polyethylene glycols, polysaccharides and phospholipids. In the examples, the undercoat comprised silicone polymer, and coating with the polymer/drug mixture was carried out by spraying a suspension in which both drug and polymer were dispersed, followed by curing of the polymer.
In our earlier specification WO-A-0101957, unpublished at the priority date hereof, we describe methods for loading drugs into polymer coated stents. The polymer coating preferably comprised a crosslinked copolymer of an ethylenically unsaturated zwitterionic monomer with a hydrophobic comonomer. The drug was intended to be delivered into the wall of the vessel in which the stent was implanted and the thickness of the coating on the stent was adapted so as to provide higher drug dosage on the outer surface of the stent. The drugs were selected from antiproliferatives, anticoagulants, vasodilators, antiinflammatories, cytotoxic agents and antiangiogenic compounds.
It is well known to those who work in the area of surfactant chemistry that it is possible to determine critical micelle concentrations by use of hydrophobic probes, which seek out the hydrophobic interior of micelles in preference to remaining in an aqueous environment. Pyrene is one such molecule. Moreover, the fluorescence intensities of various vibronic fine structures in the pyrene molecules' fluorescence spectrum shows strong environmental effects based upon the polarity of the solvent in which it is present (Kalyanasundaram, K. et al; JACC, 99(7), 2039, 1977). The ratio of the intensity of a pair of characteristic bonds (13:11) is relevant to the environment. A value for I3:I1 of about 0.63 is indicative of an aqueous environment whilst a value of about 1 is indicative of hydrophobic environment.
Matrix metalloproteinases (or matrix metalloproteases) MMPs are zinc-binding endopeptidases involved in connective tissue matrix remodelling and degradation of the extra cellular matrix (ECM), an essential step in tumour invasion, angiogenesis and metastasis. The MMP's each have different substrate specificities within the ECM and are important in its degradation. The analysis of MMP's in human mammary pathology showed that several MMP's are involved:collagenase (MMP1) which degrades fibrillar interstitial collagens; gelatinase (MMP2), which mainly degrade type IV collagen; stromelysin (MMP3) which has a wide range of substrate activities.
Tissue inhibitors of metalloproteinase (T1MPs) represent a family of ubiquitous proteins which are natural inhibitors of MMPIs. TIMP-4 is thought to function in a tissue-specific fashion in ECM hemostasis. WO-A-00/53210 suggests that TIMP-4 may be useful in the treatment of vascular diseases such as restenosis after balloon angioplasty. Local delivery of the TIMP-4, or oligonucleotide encoding TIMP-4 is suggested through injecting needles, or through a catheter used in an angioplasty intervention.
U.S. Pat. No. 5,240,958 describes a class of hydroxamic acid derivatives of oligopeptides which inhibit metalloproteinases that is are matrix metalloproteinase inhibitors, MMPIs. The compounds are useful in the management of disease involving tissue degradation, especially rheumatoid arthritis, or other arthropathies, inflammation, dermatological disease, bone resorption and tumour invasion, as well as promoting wound healing. Local delivery into a joint may be effected by direct injection. One of the exemplified compounds is batimastat. Hydroxamic acid MMP1's are shown to promote tumour regression or inhibit cancer cell proliferation in WO-A0-93/21942. In WO-A-94/10990 such compounds are shown to inhibit tumour necrosis factor (TNF) production.
In WO-A-98/25597 MMPI's are used to prevent and treat heart failure and ventricular dilation. In WO-A-99/47138, the use of MMPI's in combination with statins are used to treat vascular diseases, including inhibiting restenosis. The delivery of the MMPI is systemic, although release may be controlled. In WO-A-99/32150, MMPI's are used in combination with ACE inhibitors to slow and reverse the process of fibrosis, ventricular dilation and heart failure. In WO-A-00/04892 a combination of MMPI's and acyl-Co:Acholesterol acyltransferase (ACAT) are used to reduce smooth muscle cell (SMC) and macrophage proliferation in atherosclerotic legions.
In WO-A-95/03036 it is suggested that stents are coated with antiangiogenic drugs to inhibit tumour invasion. Examples of antiangiogenic drugs include TIMP-1, TIMP-2 and metalloproteinase inhibitors such as BB94 (batimastat). The antiangiogenic agent is delivered from a polymeric carrier.
In U.S. Pat. No. 6,113,943 it is suggested that batimastat is an angiogenesis suppressor. It is delivered in that invention from a lactic acid polymer by sustained release.
In WO-A-00/56283, polymers having metal chelating activities are said to have MMP inhibitory activity. The polymers may be coated onto a stent. It is suggested that MMP's contribute to the development of atherosclerotic plaques and post angioplasty restenotic plaques. The IVIMP inhibiting activity of the polymers is believed to be useful in inhibiting restenosis. The polymers may be coated onto a stent and may have additional pharmaceutically active agents dispersed therein, such as MMPI's, including hydroxamic acids and, specifically, batimastat. Polymers having MMPI activity are capable of chelating divalent metals, and are generally polymers of unsaturated carboxylic acids although sulphonated anionic hydrogels may be used. One example of a monomer for forming a sulphonated anionic hydrogel is N, N-dimethyl-N-methacryloyloxyethyl-N-(3-sulphopropyl)ammonium betaine. Other examples of polymers are acrylic acid based polymers modified with C10-30-alkyl acrylates crosslinked with di- or higher-functional ethylenically unsaturated crosslinking agents. There is no specific suggestion of how to provide a coating on a stent comprising both MMPI active polymer and additional therapeutic agent.
In WO-A-99/01118, antioxidants are combined with antineoplastic drugs to improve their cytotoxicity. One example of the antineoplastic drug whose activity may be increased is batimastat. One utility of the antineoplastic combination is in the treatment of vascular disease. The drug combination may be administered from a controlled release system.
The crosslinkable polymer of 2-methacryloyloxyethy1-2′-trimethyl ammoniumethyiphosphate inner salt and dodecyl methacrylate with crosslinking monomer, coated onto a stent and cured, has been shown to reduce restenosis following stent delivery for the treatment of atherosclerotic conditions. In WO-A-01/01957 mentioned above, we show that a range of drugs may be loaded onto the polymer coated stents such that delivery of the drug into adjacent tissue takes place.